1. Field of the Invention
The present invention relates to a technology for preparing high crystalline nanoporous titanium dioxide. More particularly, the present invention relates to a method of preparing high crystalline nanoporous titanium dioxide (TiO2), in which the high crystalline nanoporous titanium dioxide (TiO2), which is harmless to the human body and self-purified through the decomposition of organic matters, can be prepared in mass production at the room temperature through a simply synthesis method.
2. Description of the Related Art
A photocatalyst refers to a catalyst activated by light energy. Since the photocatalyst represents the activity and reaction mechanism in the normal temperature, the photocatalyst is distinguished from the general catalyst and can be used in a simple and small-size reactor. When light having a predetermined wavelength is irradiated onto semiconductor oxide, such as TiO2, electrons (e−) excited by the light migrate to a conduction band and holes (h+) are created and migrate to a surface of the TiO2. The holes may react with H2O or OH− on the surface of the TiO2, so that OH radicals are generated, and the OH radicals decompose the organic matters adhering to the surface of the TiO2 by oxidizing the organic matters. The TiO2 has bandgap energy of about 3.2 eV and it is generally known in the art that light having energy higher than the bandgap energy of the TiO2 among solar lights has the wavelength of 380 nm or below.
The photocatalyst has been extensively used as an environmental material to remove trace organic matters and bad smells, to restrict carcinogenic substances, to treat waste water or to remove Sox and NOx, and used in the energy field to prepare hydrogen fuel by dissolving water. In addition, the photocatalyst has great potential energy in applications thereof. For instance, the photocatalyst can be used to convert harmful components into useful components as well as to decompose harmful substances.
Representative examples of the photocatalyst are TiO2, SnO2, Fe2O3, WO3, ZnO and CdS. Although various oxides can be used as the photocatalyst, ZnO and CdS are disadvantageous in that they generate harmful Zn and Cd as they are decomposed by the light. In addition, WO3 represents the superior efficiency as the photocatalyst only for specific materials and SnO2 and Fe2O3 represent the low efficiency when they are used as the photocatalyst.
Among the above materials, TiO2 may not be changed even if the light is irradiated thereto, so the TiO2 can be semi-permanently used. In addition, the TiO2 can decompose any organic matters into CO2 and H2O by oxidizing the organic matters, so the TiO2 has been spotlighted as the photocatalyst.
The TiO2 has three crystalline phases of rutile, anatase and brookite under the normal pressure and can be transited from the brookite and the anatase phases, which are metastable phases, to the rutile phase as the temperature is increased. The brookite and the anatase having the tetragonal structures and the brookite having the orthorhombic structure are based on the TiO6 octahedral structure mainly consisting of Ti, in which the rutile shares two edges, the anatase shares four edges and the brookite shares three edges.
The rutile includes two unit cells, the anatase includes four unit cells and the brookite includes eight unit cells.
The TiO6 octahedral structure serving as the basic structure is tilted from the regular octahedral structure and the tilting degree may increase in the order of the rutile, the anatase and the brookite. When determining according to the Pauling' law, the rutile is the most stable structure in terms of energy. The anatase and the brookite have the metastable structures, which can be transited into the stable structures through the high-temperature treatment. When analyzing based on the energy band concept, the anatase and the rutile have the 3.2 eV and 3.0 eV, respectively. Therefore, when comparing with the anatase, the rutile can absorb light having the wider ultraviolet band, so it is expected that the light source employing the rutile may represent the superior light efficiency than the light source employing the anatase. However, the anatase represents the superior performance in practice.
As a cited reference of the present invention, Korean Unexamined Patent Publication No. 10-2011-0011973 discloses a method of preparing TiO2 and a method of fabricating a dye-sensitized solar cell by using the same.